The present invention relates to a lubricating system for an overhead camshaft engine (hereinafter referred to simply as xe2x80x9cOHC enginexe2x80x9d), in particular, to an effective technique applied to the OHC type of general-purpose engine, a cylinder axis of which is located with an inclination with respect to the gravitational direction.
In the prior art, an overhead valve (hereinafter referred to simply as xe2x80x9cOHVxe2x80x9d) and OHC type of general-purpose engines have been widely used as power sources for mowers, power sprayers, power generators, etc. For example, Japanese Patent Application Laid-open Publication No. Hei. 10-280932 discloses an engine of the OHV type, a cylinder axis of which is inclined in order to realize a compact size of the system. Further, Japanese Patent Application Laid-open Publication No. Hei. 8-177441 discloses an engine of the OHC type, an oil dipper of which rotates together with a crankshaft to improve a lubricating performance for a valve-operating system.
In such a general-purpose engine, a so-called splash method has been widely employed as a lubricating method of such a valve-operating system as chains, sprockets, and cams for reducing cost and size. In this splash method, an oil pump is not used, but is used the oil dipper in order to pick up a lubricating oil in an oil pan, so that splashes of the oil lubricates the system. As the oil dipper, while a paddle type is disclosed in the Publication No. Hei. 10-280932, a water mill wheel type is disclosed in the Publication No. Hei. 8-177441.
However, there was a problem of resulting in a cost up by increasing the number of components and in a complicated structure in the case of the lubricating system as described in the Publication No. Hei. 8-177441 since the oil dipper is disposed on an axis different from that of a crankshaft. In addition, there was also a problem of causing not only a large stirring resistance to become a rotational load, but also a raised oil temperature since the water mill wheel dips the lubricating oil up from the oil pan. Furthermore, there was a disadvantage that the height of the engine is increased by the height of the oil dipper.
On the other hand, the system of the Publication No. Hei. 10-280932 dips the oil up by means of the dipper mounted on a large end portion of a connecting rod, thereby lubricating the valve-operating system without increasing the number of components. In addition, this system can cause less stirring resistance, resulting in less raised oil temperature, since the paddle type of dipper moves as cutting the oil. Although, however, such a dipper can splash the oil along the circumference direction of the connecting rod, the dipper can not splash it toward a side of the connecting rod. Therefore, the valve-operating system of OHC engine can not be well lubricated by such a dipper since the valve-operating system deviates from the connecting rod in the longitudinal direction of the crankshaft.
Namely, in the OHV engine as described in the Publication No. Hei. 10-280932, the valve-operating system can be well lubricated by the paddle type of dipper since a valve-operating cam can be disposed in the vicinity of the oil dipper. In the OHC engine, however, a timing valve-operating member such as a chain or a cogged belt is offset from the connecting rod, so that the oil can not be splashed to the place of the chain by the dipper of the paddle type.
An object of the present invention is to securely supply a lubricating oil to a timing system without increasing the number of components in an OHC general-purpose engine.
In order to achieve the above mentioned object, there is provided a lubricating system of an overhead camshaft engine having a valve-operating cam provided on a cylinder head of the engine and driven in synchronization with a crankshaft via a timing system which comprises a scraper provided on a large end portion of a connecting rod of the engine in order to pick up a lubricating oil stored in a lower portion of a crankcase of the engine so as to lubricate the timing system. The scraper includes a bottom wall extending in a radial direction of the crankshaft and a side wall erected from the bottom wall.
According to the present invention, droplets of the oil can be splashed in the three-dimensional inclined direction, i.e., to the side direction of the scraper. Therefore, the droplets of the oil can be supplied to the timing system offsetted to the scraper in a longitudinal direction of the crankshaft. Thus, the timing system of the OHC engine can be securely lubricated without increasing the number of the components even though being offsetted from the scraper,
In this case, the engine may be an inclined type of OHC engine which has a cylinder axis, inclined with respect to the gravitational direction. In addition, an angle formed between the bottom wall and the side wall may be appropriately set within a range of 60xc2x0 to 90xc2x0.